Jeffrey McCord

Magnetically induced reorientation of martensite variants in constrained epitaxial Ni-Mn-Ga films grown on MgO(001)

Magnetically induced reorientation (MIR) is observed in epitaxial orthorhombic Ni-Mn-Ga films. Ni-Mn-Ga films have been grown epitaxially on heated MgO(001) substrates in the cubic austenite state. The unit cell is rotated by 45 relative to the MgO cell. The growth, structure texture and anisotropic magnetic properties of these films are described. The crystallographic analysis of the martensitic transition reveals variant selection dominated by the substrate constraint. The austenite state has low magnetocrystalline anisotropy. In the martensitic state, the magnetization curves reveal an orthorhombic symmetry having three magnetically non-equivalent axes. The existence of MIR is deduced from the typical hysteresis within the first quadrant in magnetization curves and independently by texture measurement without and in the presence of a magnetic field probing microstructural changes. An analytical model is presented, which describes MIR in films with constrained overall extension by the additional degree of freedom of an orthorhombic structure compared to the tetragonal structure used in the standard model.

Intrinsic and non-local Gilbert damping in polycrystalline nickel studied by Ti : sapphire laser fs spectroscopy

The use of femtosecond laser pulses generated by a Ti : sapphire laser system allows us to gain an insight into the magnetization dynamics on time scales from sub-picosecond up to 1 ns directly in the time domain. This experimental technique is used to excite a polycrystalline nickel (Ni) film optically and probe the dynamics afterwards. Different spin-wave modes (the Kittel mode, perpendicular standing spin-wave modes and dipolar spin-wave modes (Damon–Eshbach modes)) are identified as the Ni thickness is increased. The Kittel mode allows determination of the Gilbert damping parameter α extracted from the magnetization relaxation time τα. The non-local damping by spin currents emitted into a non-magnetic metallic layer of vanadium (V), palladium (Pd) and the rare earth dysprosium (Dy) are studied for wedge-shaped Ni films of 1–30 nm. The damping parameter increases from α = 0.045 intrinsic for nickel to α > 0.10 for the heavy materials, such as Pd and Dy, for the thinnest Ni films below 10 nm thickness. Also, for the thinnest reference Ni film thickness, an increased magnetic damping below 4 nm is observed. The origin of this increase is discussed within the framework of line broadening by locally different precessional frequencies within the laser spot region.

Evidence for a dynamic phase transition in [ Co / Pt ] 3 magnetic multilayers

A dynamic phase transition (DPT) with respect to the period

Absence of magnetic domain wall motion during magnetic field induced twin boundary motion in bulk magnetic shape memory alloys

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Kerr observations of asymmetric magnetization reversal processes in CoFe/IrMn bilayer systems

of an applied alternating magnetic field has been observed previously in numerical simulations of magnetic systems. However, experimental evidence for this DPT has thus far been limited to qualitative observations of hysteresis loop collapse in studies of hysteresis-loop area scaling. Here, we present significantly stronger evidence for the experimental observation of this DPT in a

Progress in magnetic domain observation by advanced magneto-optical microscopy

{[\text{Co}(4\text{ }\text{\AA{}})/\text{Pt}(7\text{ }\text{\AA{}})]}_{3}

Introducing artificial length scales to tailor magnetic properties

-multilayer system with strong perpendicular anisotropy. We applied an out-of-plane time-varying (sawtooth) field to the

Control of saturation magnetization, anisotropy, and damping due to Ni implantation in thin Ni81Fe19 layers

{[\text{Co}/\text{Pt}]}_{3}

Tuning of magnetization dynamics by ultrathin antiferromagnetic layers

multilayer in the presence of a small additional constant field,

Dynamic anisotropy in amorphous CoZrTa films

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